The invention relates to a rotary sheet feeder with a feeder frame on which there are disposed an upper feeder table adapted to be loaded with imbricated stacks of sheets and which comprises a first belt conveyor with rollers, a reversing drum, a lower withdrawal table comprising a second belt conveyor with rollers, the receiving side of which is disposed opposite the delivery portion of the first belt conveyor and, disposed at intervals from one another, flexible guide means for pressing the sheets against the reversing drum and adapted to the existing sheet stack height, said guide means having one end supported above the upper feeder table and forming with the reserving drum an intake gusset, while their bottom ends are fixed via elastically extensible elements on respective rods connected to the feeder frame.
In the case of such a rotary sheet feeder which is known from DE-A-1 960 543, the flexible guide means for pressing the sheets against the reversing drum consist on the one hand of belts which revolve endlessly about rollers situated at intervals over the axial length of the reversing drum and of which some are so mounted for elastic deflection that adaptation to whatever is the given height of the imbricated stack of sheets is assured while maintaining the pressure which is applied by the belts. In addition, between these endless guide belts there are provided cable-like guides each of which has one end supported above the upper feeder table, forming an intake gusset together with the reversing drum, while their bottom ends are connected via springs to fixed points on the frame side, so that by stretching these springs the cable-like guides can likewise be adapted to the height of the stack sheet.
In the case of the prior art rotary sheet feeder, the speed of the sheet stack at the table end is somewhat less than that of the guide belts which press the stack of sheets against the reversing drum because the outer end of the stack in contact with the guide belts travels in an arc of greater radius than that of the inner end of the stack which is adjacent the reversing drum. The cable-like guides consist of a low-friction material and therefore do not impede the travel of the outer end of the stack. By reason of this relative speed between the guide belts and the stack, it is possible for the imbricated arrangement to be disturbed, which becomes translated into irregular distances between the sheets at the withdrawal table. The adjustment of an identical speed from time to time in order to reduce the relative speed to zero is very complicated both in terms of apparatus and also with regard to control processes.
It is also known from GB-C-604653 to provide at a distance from the reversing drum of a rotary sheet feeder curved guide members which are mounted on the feeder frame. These guide members have on the one hand quite considerable friction and only permit of adaptation to different heights of sheet stacks after complicated adjustment operations have been performed.
An object of the present invention is to reduce or alleviate the problem of disturbance of the stacks of sheets which arises from the difference in speeds between the radially inner and outer ends of the stacks.